Transcriptional regulation in cells is a complex biological process. One basic principle is regulation by posttranslational modification of histone proteins, namely histone proteins H2A/B, H3 and H4 forming the octameric histone core complex. These complex N-terminal modifications at lysine residues by acetylation or methylation and at serine residues by phosphorylation constitute part of the so called “histone code” (Strahl & Ellis, Nature 403, 41-45, 2000). In a simple model, acetylation of positively charged lysine residues decreases affinity to negatively charged DNA, which now becomes accessible for the entry of transcription factors.
Histone acetylation and deacetylation is catalysed by histone acetyltransferases (HATs) and histone deacetylases (HDACs). HDACs are associated with transcriptional repressor complexes, switching chromatin to a transcriptionally inactive, silent structure (Marks et al. Nature Cancer Rev 1, 194-202, 2001). The opposite holds true for HATs which are associated with transcriptional activator complexes. Three different classes of HDACs have been described so far, namely class I (HDAC 1-3, 8) with Mr=42-55 kDa primarily located in the nucleus and sensitive towards inhibition by Trichostatin A (TSA), class II (HDAC 4-7, 9, 10) with Mr=120-130 kDa and TSA sensitivity and class III (Sir2 homologues) which are quite distinct by their NAD+ dependency and TSA insensitivity.
Cancer chemotherapy was established based on the concept that cancer cells with uncontrolled proliferation and a high proportion of cells in mitosis are killed preferentially. Standard cancer chemotherapeutic drugs finally kill cancer cells upon induction of programmed cell death (“apoptosis”) by targeting basic cellular processes and molecules, namely RNA/DNA (alkylating and carbamylating agents, platin analogs and topoisomerase inhibitors), metabolism (drugs of this class are named anti-metabolites) as well as the mitotic spindle apparatus (stabilizing and destabilizing tubulin inhibitors). Inhibitors of histone deacetylases (HDIs) constitute a new class of anti cancer drugs with differentiation and apoptosis inducing activity. By targeting histone deacetylases, HDIs effect histone (protein) acetylation and chromatin structure, inducing a complex transcriptional reprogramming, exemplified by reactivation of tumor suppressor genes and repression of oncogenes. Beside effecting acetylation of N-terminal lysine residues in core histone proteins, non-histone targets important for cancer cell biology like heat-shock-protein 90 (Hsp90) or the p53 tumor suppressor protein exist. The medical use of HDIs might not be restricted to cancer therapy, since efficacy in models for inflammatory diseases, rheumatoid arthritis and neurodegeneration was shown.
Benzoyl or acetyl substituted pyrrolyl propenamides are described in the public literature as HDAC-inhibitors, whereas the connectivity of the acyl-group is at position 2 or 3 of the pyrrole scaffold. (Mai et. al., Journal Med. Chem. 2004, Vol. 47, No. 5, 1098-1109; or Ragno et al., Journal Med. Chem. 2004, Vol. 47, No. 5, 1351-1359). Further pyrrolyl substituted hydroxamic acid derivatives are described in U.S. Pat. No. 4,960,787 as lipoxygenase inhibitors or in U.S. Pat. No. 6,432,999 as cyclooxygenase inhibitors or in EP570594 as inhibitors of cell growth.
Addressing the remaining need in the art for novel, well-tolerated and more efficacious inhibitors of HDACs, the international applications WO 2005/087724, WO 2007/039403 and WO 2007/039404 describe N-hydroxy-acrylamide derivatives of N-sulphonylpyrroles as HDAC inhibitors.
WO 2005/087724, WO 2007/039403 and WO 2007/039404 also disclose a process for the preparation of said N-hydroxy-acrylamide derivatives.
This preparation process comprises in the last step the synthesis of N-hydroxy-acrylamide derivatives starting from the corresponding acrylic acids. During said synthesis, the corresponding acrylic acid derivative is coupled with O-(tetrahydro-2H-pyran-2-yl)hydroxylamine by the reaction with an amide linking reagent (EDCxHCl and HOBtxH2O). After removal of the protecting group by stirring with an acid ion exchange resin, the respective N-hydroxy-acrylamide derivative is obtained:

The use of O-(tetrahydro-2H-pyran-2-yl)hydroxylamine and EDCxHCl is, however, a disadvantage not only under cost aspects but also because these reagents are not available in large quantities. Furthermore, O-(tetrahydro-2H-pyran-2-yl)hydroxylamine is explosive and it is necessary to remove the byproducts an additional purification step, e.g. column chromatography.
An object of the invention therefore is to provide a commercially attractive, less expensive but at least equally effective process for preparing N-hydroxy-acrylamide derivatives of N-sulphonylpyrrole compounds, which derivatives have HDAC inhibitory activity, which allows obtaining the reaction product in fewer steps and with high yield and purity.